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2016-08-04

Measuring Building Substructures: Solutions to‘First Year’ Introductory Level ExaminationQuestionsTony CunninghamDublin Institute of Technology, tony.cunningham@dit.ie

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Recommended CitationCunningham, Tony, "Measuring Building Substructures: Solutions to ‘First Year’ Introductory Level Examination Questions" (2016).Other Resources. 60.http://arrow.dit.ie/beschreoth/60

Measuring Substructure Work 1

MEASURING BUILDING SUBSTRUCTURES: -

SOLUTIONS TO ‘FIRST YEAR’ INTRODUCTORY LEVEL

EXAMINATION QUESTIONS

Tony Cunningham

School of Surveying and Construction Management

Dublin Institute of Technology

Introduction

The measurement of substructure works to simple domestic type buildings is a logical starting point

for students to commence the process of taking-off building quantities. Substructure work is typically

the first class of work to be explained in textbooks dealing with both construction technology and

building measurement. However, substructure work is often one of the most challenging elements to

measure. This element is unique, in that it contains both vertical (rising walls) and horizontal elements

(ground floor slabs), and comprises work from a number of separate work sections and trades (e.g.

excavation and earthworks, concrete work, brickwork and blockwork, waterproofing and

occasionally aspects of woodwork, The element also contains works which are measured in linear

metres (dpcs for example), square metres (e.g. blinding and powerfloating), and cubic metres (e.g.

concrete foundations). Examiners may be of the view that if the candidate can demonstrate the ability

to measure substructures that they should be able to successfully apply the principles of measurement

to other areas of work. The task of measuring substructures is, as a result, a regular topic in first year

building measurement and quantity surveying examinations.

In this paper, the author demonstrates the process of measuring basic substructure designs. The

approach taken involves providing solutions to a sample of four Irish Department of Education

Technological Certificate: Builders’ Quantities Intermediate Stage examinations. These three-hour-

long State examinations, which ceased in 2007, required candidates to answer two compulsory

measurement questions, one of which almost always involved a substructure. The measurement

questions accounted for 80% of the marks, (40 marks each). Candidates were also required to answer

two other short questions (10% each) relating to various theoretical aspects of quantity surveying

practice. The marking scheme above, indicates that each of the measurement questions should take

approximately 75 minutes to answer. Completing the questions within this time frame is both

challenging and pressurised.

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The Worked Examples

The worked examples are measured in accordance with the Irish Agreed Rules of Measurement

(ARM4). Different rules may apply under other standard methods of measurement. Candidates taking

these examinations were required to enter all dimensions on dimension sheets which were provided.

Readers are therefore expected to be familiar with traditional ‘paper based’ taking-off procedures.

These procedures are explained in the following papers An Introduction to Taking Off Building

Quantities: an Irish Approach http://arrow.dit.ie/beschreoth/30, Measuring Building Perimeters and

Centrelines - Worked Examples http://arrow.dit.ie/beschreoth/43, and Composing Descriptions for

Bills of Quantities in Accordance with ARM4 – Worked Examples http://arrow.dit.ie/beschreoth/44.

The worked examples are presented in order of increasing difficulty as the plans become more

complex. Explanatory notes on ARM4 rules are presented to support the first worked example. In the

interest of brevity these notes are not repeated for the subsequent questions, but apply nonetheless.

1992 – A Plain Rectangular Building

The Question

Take off the quantities for the substructure to damp proof course level. (40 marks)

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Although this is a straight-forward substructure layout which would be suitable for a garage or similar

non-habitable outbuilding, the task required the candidates to take off the complete substructure.

Candidates were not required to square the dimensions. As the candidates were not permitted to use

the ARM, they were expected to remember what items needed to be measured and the various

measurement and coverage rules governing these. The candidates would also have been expected to

make certain assumptions regarding whether particular works were necessary. For example stripping

of topsoil has not been measured in this example on the assumption that it is not required to be

preserved, this assumption avoids the need to measure the items relating to stripping, preserving and

spreading the topsoil, thereby speeding up the take-off process. All such assumptions should,

however, be checked with the architect and documented on a query sheet.

In this instance it would be prudent to compile a ‘to-take’ list of the items to be measured. This will

help to organise an effective take-off approach and reduce the risk of accidentally leaving out items

to be measured. A to-take list showing ARM4 references and units of measurement to answer this

question would include:

Reduce level excavation; - assumed there is no

requirement to preserve any topsoil.

m3 D22.3.7.4.

Trench excavation m3 D22.3.9.

Disposal of surface water Item D24.3.8.10.

Disposal of surplus excavated material m3 D24.3.10.

Backfilling trenches with excavated material m3 D24.4.11.16.

Backfilling to make up levels m3 D24.4.12.16.

Hardcore beds m3 D24.4.12.16.

Blinding hardcore beds m2 D24.5.13.

Concrete strip foundations m3 F36.4.0.0.2.

Concrete ground floor slabs m3 F36.9.1.

Powerfloating floor slab m2 F38.2.6.

Rising Walls m2 G48.2.1

Labours on brickwork Item G48.7.2

DPC m G52.3.5.2.3.

DPM horizontal m2 I66.2.1.1.

DPM perimeter kerb m I66.10.5.

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Reduce level excavation is measured in m3 classifying the depth as ≤ 2.00m or exceeding 2.00m in

2m increments. Reduce levels refers to the excavation required to reach the formation level i.e. the

bottom of the hardcore bed - which is 150mm below ground level. The measurements are taken to

the footprint of the building which extends to the outer edge of the foundations. This requires the

width of the rising walls (215mm) plus the projection of the ‘toe’ of the foundation (155mm) to be

added at both ends (2/) to the (internal) dimensions shown on the plan.

Trench excavation is also measured in m3 classifying the depth as ≤ 2.00m or exceeding 2.00m in

2m increments. The trench is measured along its centreline, and its depth is calculated from formation

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level (600-150mm) to base of the concrete foundation. Note that the standard formula for adjusting

perimeters, four times twice the distance moved, can be simplified when moving to the centreline

of a work item to four times the item’s width/thickness, - the twice and half the thickness cancel each

other out! Note also that where the dimensions relate to the inside of a building (as here) the centreline

adjustments is added to the internal perimeter length.

Disposal of surface water: an item is taken to allow the contractor the opportunity of removing

rainwater on the site and in the excavations.

Disposal of surplus excavated material: material removed from site is measured in m3. The location

of the tip is usually at the Contractor’s discretion. There are a number of approaches that may be used

to measure ‘cartaway’. As the trenches are backfilled on both sides of the rising walls it seems that

measuring the volume of earth displaced by the foundations, rising walls and hardcore bed is the most

straightforward method of calculating this quantity. Note the re-use of the trench centreline

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measurement in calculating the foundations and rising wall. An alternative approach is to add up all

the excavation and deduct any backfilling. Note, no allowance is made for bulking of the excavated

material when measuring this class of work.

Backfilling is measured in m3 stating whether it exceeds or does not exceed 250mm thick. Details of

treatment of the fill such as compacting in 225mm thick layers must be given in the description.

Excavated material is commonly used to backfill voids left by excavation operations. In trenches this

occurs between the rising wall and the trench side above the top of the foundation. In this case the

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both sides of the trench are backfilled –therefore the width of the fill is obtained by subtracting the

rising wall’s thickness from the trench width.

Additional filling is required to make up levels on the outside of the wall between the top of the

trench and ground level (see the red box on the thumbnail sketch above). Note how the internal

perimeter is adjusted to move to the centreline of this filling. The distance moved is 215 (Wall) plus

78mm (half the ‘toe’ projection) and is adjusted for each corner (4/2/293mm)

Hardcore a 150mm hardcore bed is required below the ground floor slab and is classified as making

up levels and is measured in m3 stating the average thickness as exceeding or not exceeding 250mm

thick. Hardcore descriptions must specify the kind and quality of the materials and any treatments

such as compacting. The measurements are taken within the walls producing a value which is often

referred to as the ‘gross internal floor area’

Surface treatments including blinding filling with sand is measured in m2. Note that blinding sloping

surfaces are measured separately.

Concrete Work is measured in accordance with section F of ARM. and is measured in cubic metres.

Concrete particulars state the kind and quality of materials; any performance or mix details and any

Measuring Substructure Work 9

testing requirements. In this question the concrete mix proportions are specified. Concrete is typically

billed in order of increasing concrete strengths.

Concrete foundations must state if they are poured on or against earth or unblinded hardcore as in

these instances a large proportion of the fill will seep into the surrounding ground strata. The estimator

Measuring Substructure Work 10

will need to take this into consideration when pricing this class of work. Note the work is measured

on the centreline of the trench.

Concrete ground floor slabs are described as beds and classified as either not exceeding, or

exceeding, 150mm thick.

Surface Treatments such as power floating is measured in m2.

Measuring Substructure Work 11

Brick rising walls are measured in accordance with Section G of ARM in m2. In answering this

question candidates should have provided the following particulars in their brickwork descriptions:

the kind, quality and size of the bricks; the type of bond; and the composition and mix of mortar. As

the work is covered up there are no surface finish or pointing requirements. The work is classified as

walls in trenches stating the thickness (215mm). The walls are measured on the centreline of the

trench. An Item is taken for labours on brickwork which includes various tasks such as cutting,

forming angles and ends, raking out joints and building in ends.

Damp proof courses not exceeding 225mm wide are measured in linear metres; where these exceed

225mm they are measured in m2 with laps stated in the description.

Damp proof membrane.is measured in m2 in accordance with the Roofing Cladding and

Waterproofing (Section I) of ARM, within the Waterproof and Gas Proof Non-metal Flexible Sheet

Covering sub-section. The information to be provided in damp proofing coverings states: the kind,

quality and thickness of the materials; the number of layers and extent of laps; the nature of the base

Measuring Substructure Work 12

on which the material is applied, and any underlay and insulation. Damp proofing is categorised as

(1) horizontal, (2) sloping 15-45 degrees, (3) sloping over 45 degrees – stating the slope, and (4)

vertical. Membranes are further categorised as either exceeding or not exceeding 300mm wide,

identifying whether the work is curved. A cautious approach has been taken in measuring the

perimeter upstand and lap under the damp proof course as a separate kerb. Kerbs are described in

detail stating the girth in stages of 150mm. Many surveyors, however, take the view that the upstand

is not a separate activity from the general damp proofing and include it with the horizontal damp

proofing activity.

2001 A ‘T’ Shaped Building

The Question

Measure only the following items below DPC level shown in Figure 1 and calculate the net

quantities in the units indicated.

a. Excavate topsoil average 150mm deep. Sq.m.

b. Excavate foundation trenches Cu.m.

c. Excavate to reduced level Cu.m.

d. Disposal of excavated material off site Cu.m.

e. Concrete in foundations Cu.m.

f. 100mm thick concrete blockwork in skins of hollow wall Sq.m.

g. 100mm wide DPC M

General Commentary

This question involves taking off and squaring seven items in the substructure, (the previous worked

example contained 16 items). The question mainly focuses on the candidates’ ability to calculate

quantities derived from perimeter and centreline calculations. Candidates should use the overall

building dimensions (9000 and 5300) to calculate the external perimeter. Submissions using the less

efficient ‘around the house’ approach i.e. totalling the eight dimensions on the drawing would

probably be marked down. The ‘overall’ approach also demonstrates the candidates’ understanding

that the clipped corners can be ignored when measuring perimeters. Note, however, that the figures

used to calculate the overall width of the building (5300) must be shown as a side cast (1700 + 3600).

The question also examines the candidates’ ability to calculate quantities relating to plan areas (parts

a and c: topsoil strip and reduce level dig). These require candidates to measure the area of the topsoil

stating its average thickness. This value can be labelled (TOT A) and repeated to calculate the volume

of the reduce level dig, - note this technique (CUBE X). The topsoil is measured to the footprint of

the building which extends to outer edge of the projecting ‘toe’ of the foundation. The approach taken

Measuring Substructure Work 13

below is to measure overall and then adjust for the complications, (i.e. deduct for the two set-back

‘clipped’ corners at the top of the plan). The figured dimensions of the clipped corners are used,

without adjustment, when deducting these the areas.

With regard to part (f) and (g), although the detail indicates brickwork, the question requests

candidates to measure 100mm blockwork and this has been demonstrated here. A query sheet would

confirm this discrepancy between the drawing and the bill of quantities. As the two skins of the cavity

wall are positioned an equal distance on either side of the centreline of the foundation, the centreline

can be twiced (this establishes the length of the dpcs) and multiplied by the height of the rising walls

to produce the blockwork quantity. Note that the coverage rules of ARM4 state that the term ‘walls’

includes skins of hollow walls.

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2000 A building with set-back corners and a recessed ‘bight’

The Question

Measure only the following items below DPC level shown in Figure 1 and calculate the net

quantities in the units indicated.

i. Excavate topsoil average 150mm deep. Sq.m.

ii. Excavate to reduced level Cu.m.

iii. Excavate foundation trenches starting at reduced level Cu.m.

iv. Disposal of excavated material off site Cu.m.

v. Concrete in foundations Cu.m.

vi. 200mm thick concrete blockwork in rising walls Sq.m.

vii. 50 thick sand blinding Sq.m.

General Commentary

This question again involves measuring seven items, but there is a greater emphasis here in calculating

quantities relating to areas on the plan.

Candidates were required to measure areas based on the ‘footprint’ (parts i and ii) and the ‘gross

internal floor area’ of the building (part vii). The presence of clipped corners and a recess or ‘bight’

results in a plan shape that is quite complicated. In dealing with this layout, it is advisable to measure

overall in the first instance and then adjust for the various complications, - an approach that has been

described as a ‘golden’ rule of measurement.

Dealing with ‘clipped’ corners is relatively straight forward. The plan dimensions for the adjustment

of the set-back are constant. Therefore, in moving outwards they can be applied to the topsoil, and

moving inwards they apply to the floor slab.

Adjustments for recesses or ‘bights’, on the other hand, are variable in their width but constant in

their depth. So, when moving outwards to adjust for the topsoil the width of the bight tightens by the

‘toe’ of the foundation on either side (2/175). Similarly, when adjusting for floor slab, the width of

the bight expands to include the width of the wall on both sides (2/400). Note the adjustment for the

depth of the bight remains constant in both cases (1500mm).

In calculating the perimeter of the building and associated girthings, candidates must have taken

account of the depth of the bight. The perimeter formula here is expressed as twice times the sum of

the overall length, width and projections. Again, the figures used to calculate the overall length,

width and the set-back to the top right side of the building must be shown as side casts.

Measuring Substructure Work 19

Note how the external perimeter is adjusted when calculating the volume of the backfill on the inside

and outside of the rising walls in the trench and the area of the 200mm blockwork (part vi), which is

adjusted using the formula four times twice times the distance moved.

Measuring Substructure Work 20

Note that process of checking the squaring by somebody else is demonstrated in this example.

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2007 A Building with Internal Walls

The Question

Measure the following items below DPC level shown in Figure 1 and calculate the net quantities in

the units indicated.

a) Excavate topsoil average 150mm deep. Sq.m.

b) Excavate foundation trenches starting from stripped level Cu.m.

c) Concrete to foundation trenches Cu.m.

d) Concrete to floor slab Cu.m.

e) 100mm thick brickwork internal walls Sq.m.

f) 100mm thick brickwork external leaf of cavity wall Sq.m.

g) 150 mm thick blockwork internal leaf of cavity wall Sq.m.

General Commentary

This question involves measuring the seven items above. The layout contains a clipped corner, a

bight, and foundations to both external and internal walls.

The additional issues involved in this layout requires candidates to measure foundations to partition

walls and to deal with the effects of angles and intersections on the internal foundations and also with

junctions between the internal and external foundations. In addition, works relating to the ground

floor slab must take account of the rising walls which penetrate the various constituents of the floor

structure.

It may be noted that when measuring the partitions that the lengths of the foundation trenches do not

equal the lengths of the walls. This is due to the trenches overlapping each other at the various

junctions. On external foundations, the extent of the projecting ‘toe’ is subtracted from the adjoining

internal foundation trench. Where internal partitions intersect, the width of the intersecting foundation

is deducted. Note also, that in measuring the partitions, it is possible to envision a simplified layout

by realigning the partitions running top to bottom on the plan to form a continuous ‘crosswall’ (see

item b).

With regard to the two 100mm brickwork items (items e and f), these would normally be aggregated

and measured together. The question, however, requires the two to be measured separately and this

instruction has been followed here.

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In Summary

Measuring substructures is a frequent examination topic on first year quantity surveying programmes.

These examinations remain, to a great extent, paper based and require the candidates to demonstrate

sound measurement procedure in describing and quantifying work. In this paper the Author presents

solutions to a sample of four State examinations. The intention is to demonstrate how descriptions,

dimensions and the supporting ‘waste calculations’ and annotations may be set out. It is

acknowledged that there are many ways to arrive at a quantity, but examiners must be able to follow

the candidates thought process without undue difficulty. Demonstrating a clear and effective approach

is the key to obtaining high marks. Sound practice holds that all steps in performing calculations

should be clearly recorded, and that mental arithmetic should be avoided. Candidates should also

avoid presenting cramped / sloppy work.

The substructure examination questions selected here show the importance of the ability to measure

and adjust surface areas and perimeters accurately and effectively. This skill is acquired through

practice. It is hoped that the worked examples presented here will help students to develop these skills

and develop their ability to apply the principles to other situations.

Further Reading

Readers are recommended to consult Chapter Four of Seeley and Winfield’s Building Quantities

Explained Irish Edition. (Hore, A.V. O’Kelly, M. and Scully, R. eds. (2009) Palgrave McMillan,

Basingstoke.) This Chapter sets out a full substructure measure with accompanying explanations and

commentary.